A new catalyst technology has developed which provides for the modification and/or control over the properties and characteristics of a polymer. This technology principally involves the use of single-site catalysts to produce a broad range of polymers generally having a narrow molecular weight distribution and a narrow composition distribution. These catalysts are generally in the field of transition metal catalysis. The art has focused on the type of catalyst and catalyst system employed and methods for their manufacture and use in polymerization catalysis.
It is desirable in many polymerization processes, particularly a gas phase process, to use a supported catalyst. Generally these catalyst systems include a metallocene and alumoxane supported on the same carrier, such as silica, and subsequently dried to a powder. For example, U.S. Pat. No. 4,937,217 generally describes a mixture of trimethylaluminum and triethylaluminum added to an undehydrated silica then adding a metallocene to form a dry catalyst. EP-308177-B1 generally describes adding a wet monomer to a reactor containing a metallocene, trialkylaluminum and undehydrated silica. U.S. Pat. Nos. 4,912,075, 4,935,937 and 4,937,301 generally relate to adding trimethylaluminum to an undehydrated silica and then adding a metallocene to form a dry supported catalyst. Similarly, U.S. Pat. Nos. 5,008,228, 5,086,025 and 5,147,949 generally describe forming a dry supported catalyst by the addition of trimethylaluminum to a water impregnated silica then adding the metallocene. U.S. Pat. No. 4,914,253 describes adding trimethylaluminum to undehydrated silica, adding a metallocene and then drying the catalyst with an amount of hydrogen to produce a polyethylene wax. U.S. Pat. Nos. 4,808,561, 4,897,455 and 4,701,432 describe techniques to form a supported catalyst where the inert carrier, typically silica, is calcined and contacted with a metallocene(s) and a activator/cocatalyst component. U.S. Pat. No. 5,238,892 describes forming a dry supported catalyst by mixing a metallocene with an alkyl aluminum then adding undehydrated silica. U.S. Pat. No. 5,240,894 generally pertains to forming a supported metallocene/alumoxane catalyst system by forming a metallocene/alumoxane reaction solution, adding a porous carrier, evaporating the resulting slurry to remove residual solvent from the carrier. These references all concern the combination of a metallocene and alumoxane on one support or hydrolyzing an aluminum alkyl in situ on one support with a metallocene catalyst compound.
It would be highly desirable to have a polymerization catalyst system that could be modified easily without having to reformulate the entire catalyst system. Thus, a need exists in industry for an improved polymerization catalyst system and method for producing such a catalyst system.